Notes about the XTML file extension:
Incorrect file associations could be the result of underlying issues within your PC system. As such it is highly recommended to scan your PC for invalid registry entries, unused processes and other unfavourable system settings to identify slowdown issues.
The XTML file type is primarily associated with 'XML4web' by Altair Communications Corporation. [Link is to a Czech Republic site.] This is extension added to virtual files generated by the XML4web content management system. The only case when this file can physically exist is when someone saves the XML4web result. In such case treat the file as HTML.